1. Field of the Invention
The present invention relates to an endoscope having a signal cable. More particularly, the present invention relates to an endoscope in which various circuit elements and parts can be protected from damages even when a signal cable is pulled abruptly or forcibly, and which can have a simplified structure.
2. Description Related to the Prior Art
An endoscope has a section of an elongated tube for entry in a body cavity of a patient. The elongated tube includes a head assembly with a rigid tip, a steering device and a flexible device arranged in a proximal direction. A distal surface of the head assembly includes an imaging window, lighting window, distal instrument opening, end nozzle and the like. A solid state imaging unit is disposed on an inner surface of the head assembly, and positioned at the imaging window. A light guide device is disposed on the inner surface of the head assembly, and positioned at the lighting window. The steering device is constituted by plural link elements connected with one another. Wires of the steering device are pulled to bend the head assembly in a desired direction. The flexible device has such a length as 1-2 meters for reach of the head assembly to an object of interest in a body cavity.
The solid state imaging unit includes a lens system and an imaging device. The lens system includes a lens, prism and other optical elements. The imaging device is a CCD or other image sensor for photoelectrically converting image light focused by the lens system into an image signal. There are a flexible circuit board and an additional circuit board. A signal cable connects the imaging device to the flexible circuit board and the additional circuit board. Electronic circuit elements are mounted on the flexible and additional circuit boards for driving the imaging device. A processing apparatus is connected by the signal cable to the flexible and additional circuit boards, and supplied with a signal from the solid state imaging unit. The processing apparatus processes the signal in the image processing, and drives a monitor display panel to display an image of an object of the body cavity, for example a lesion of tissue.
The signal cable from the solid state imaging unit to the processing apparatus is a multi-core cable. As the signal cable extends for a full length of the elongated tube, the signal cable is pushed and pulled at each time that the elongated tube is looped, steered or otherwise bent. There are connecting portions where the signal cable is connected to the flexible circuit board. Stress of the push and pull may drop the signal cable from the connecting portions.
Various suggestions have been made for preventing drop of the signal cable. JP-A 5-261064 discloses the endoscope in which the signal cable is soldered to one end of the flexible circuit board. The flexible circuit board is bent in a channel shape to extend around a soldered portion of the signal cable. A shield tape and insulation tape are used to cover the flexible circuit board. Adhesive agent is filled in an inner space of the flexible circuit board and prevents deformation by hardening. The endoscope includes a circuit board and a support sleeve or connection sleeve. The circuit board has a portion where the signal cable is attached, and is fixedly secured to the support sleeve by use of a spacer plate and a screw. Even when the signal cable is pulled strongly, the circuit board does not move. Stress of distortion or inclination exerted by the signal cable to the circuit board is not transmitted to the imaging device or the lens system, because absorbed by the circuit board with flexibility.
JP-A 9-146011 discloses the solid state imaging unit in which encapsulant is used to encapsulate the connecting portions between the flexible circuit board and the signal cable.
JP-A 2008-118568 discloses the solid state imaging unit in which a rigid housing or reinforcing frame contains the imaging device and a portion of the flexible circuit board for mounting circuit elements. The adhesive agent is filled in an inner space of the processing apparatus. A thermal contraction tube is used to cover the rigid housing and a tip of the signal cable soldered on the flexible circuit board. An inner space of the thermal contraction tube is filled with the adhesive agent for sealing tightly.
In the solid state imaging unit of JP-A 5-261064, there is a shortcoming in complicated handling for attaching the circuit board to the support sleeve with the screw. In the solid state imaging unit of JP-A 9-146011, stress of push and pull in the signal cable is transmitted to the flexible circuit board or the connecting portions of the flexible circuit board. The connecting portions of soldering between the signal cable and the flexible circuit board or the connecting portions between the flexible circuit board and the imaging device may receive stress applied to the flexible circuit board. It is likely that peeling or breakage may occur in a weak portion of any one of those elements.
According to the solid state imaging unit of JP-A 2008-118568, a size of the rigid housing must be predetermined according to a size of the imaging device, as the imaging device is contained in the rigid housing. Various elements including the imaging device and others associated therewith are technically complicated in compliance with requirement for the endoscope, for example high definition, reduction of a diameter, use with an autoclave system, and the like. If the size of the endoscope is enlarged with a larger number of functions of the imaging device and other elements, the size of the rigid housing for containment will be enlarged. A diameter of the head assembly of the elongated tube will be larger. There will arise a problem in that physical stress of a patient will be high in use of the endoscope.